Method of and apparatus for producing a vehicle movement control signal in response to sensing the direction of travel of a vehicle

ABSTRACT

A pair of tachometers are operatively engaged with the drive mechanism of a vehicle. The tachometers are aligned relative to one another such that if the vehicle is traveling in a forward direction the signal provided at the output of the first tachometer leads the signal provided at the output of the second tachometer by a first predetermined phase angle, and if the vehicle is traveling in the reverse direction, the signal output of the second tachometer leads the signal output of the first tachometer by a second predetermined phase angle. Apparatus is included for sensing the relative phase of the respective signals provided at the outputs of the tachometers. In response to sensing that the output signal of the first tachometer leads the output signal of the second tachometer by the first predetermined phase angle, a vehicle movement control signal is provided which informs the vehicle drive mechanism that it is safe for the vehicle to continue its movement. In the event the apparatus senses that the output signal of the second tachometer leads the output signal of the first tachometer by the second predetermined phase angle, the provision of the vehicle movement control signal is inhibited.

United States Patent 1 Matty METHOD OF AND APPARATUS FOR PRODUCING AVEHICLE MOVEMENT CONTROL SIGNAL IN REsPoNsE TO SENSING THE DIRECTION OFTRAVEL OF A VEHICLE [75] Inventor: Thomas C. Matty, lrwin, Pa.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Jan. 26, 1972 [21] Appl. 'No.: 220,829

[52] US. Cl 317/5, 307/232,.318/683,

324/83 A, 340/52 R, 340/271 [51] Int. Cl. H02p 15/00 [58] Field ofSearch 104/151; 105/61;

307/232, 148, 122,269, 253; 317/5, 33; 318/8, 99, 683; 324/165, 83 A, 83D, 86; 340/52 R, 62, 263, 271

[ 1 Jan. 1,1974

Primary ExaminerGeorge E. A. Halvosa Assistant Examiner-Stephen G. KuninAtt0rneyFv H. Henson et al.

[57] ABSTRACT A pair of tachometers are Operatively engaged with thedrive mechanism of a vehicle. The tachometers are aligned relative toone another such that if the vehicle is traveling in a forward directionthe signal provided at the output of the first tachometer leads thesignal provided at the output of the second tachometer by a firstpredetermined phase angle, and if the vehicle is traveling in thereverse direction, the signal output of the second tachometer leads thesignal output of the first tachometer by a second predetermined phaseangle. Apparatus is included for sensing the relative phase of therespective signals provided at the outputs of the tachometers. Inresponse to sensing that the output signal of the first tachometer leadsthe output signal of the second tachometer by the first prede- 5References Ci d termined phase angle, a vehicle movement control sig-UNITED STATES PATENTS nal is provided which informs the vehicle drivemecha- 299 l 7 H v 32 65 nism that it is safe for the vehicle tocontinue its 23 1 2; x23 4/1 movement. In the event the apparatus sensesthat the 3559O08 U197] Stut at l output signal of the second tachometerleads the out- 304,496 2/1967 Lorenzmm: 307 232 x P Signal of the firsttachomfiter by the Second P termined phase angle, the provision of thevehicle FOREIGN PATENTS OR APPLICATIONS movement control signal isinhibited. 1,298,297 6/1969 Germany 324/165 8 Claims, 15 Drawing FiguresTACH ,53 ALARM AND 9 BRAKING TAcH PATENTED JAN 1 I974,

sum 1 or 2 RM AND BRAKING FIGS 4L ALA METHOD OF AND APPARATUS FORPRODUCING A VEHICLE MOVEMENT CONTROL SIGNAL IN RESPONSE TO SENSING THEDIRECTION OF TRAVEL OF A VEHICLE CROSS REFERENCE TO RELATED APPLICATIONSReference is made to US. Pat. No. 3,600,604 by George M. Thomebooth,which is assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION There is a need to sensethe direction oftravel of a vehicle operative in an automated vehicle control system sothat the safety of the passengers is assured at all times. If a vehicleleaves a first control block and enters a second control block, and thenbegins to roll-back into the first control block, the possibility existsthat the vehicle could collide with a following vehicle. To protectagainst such occurrences, direction of travel sensing apparatus isneeded.

Generally, prior art apparatus for sensing the direction of travel ofthe vehicle comprised a mechanical mechanism that was rather large anddifficult to align. There is a need to provide electronic directionsensing apparatus which is relatively compact, easy to manufacture, hasa low production cost, and which is extremely reliable. It is the objectof this invention to provide a direction sensing mechanism of the lattertype.

SUMMARY OF THE INVENTION According to the teachings of the presentinvention, a method and system for sensing the direction of movement ofa vehicle is provided. There are means for providing first and secondsignals displaced relative to one another in a first predetermined phaserelationship in response to the vehicle moving in a first direction,with the first and second signals being displaced relative to oneanother in a second predetermined phase relationship in response tothevehicle moving in the opposite direction. There are also included meansfor providing a vehicle movement control signal in response to sensingthat the first and second. signals are displaced from one anotheraccording to the first predetermined phase relationship. Also includedare means for inhibiting the provisions of the vehicle movement controlsignal in response to sensing that the first and second signals aredisplaced from one another according to the second predetermined phaserelationship.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial representationof a vehicle traveling along a vehicle travel path.

7 FIGS. 4A through 4L are wave-shape relationship diagrams helpful inthe understanding of the operation of a a t ,i tretssimfl .31-

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is generallyshown a vehicle 2 supported in part by wheels 3 and 4, and which travelsalong a vehicle travel path 5 in a first or forward direction from thepoint A to the point B. If the vehicle 2 for one reason or anotherreverses its direction of travel and moves from the point B to the pointA, this will be termed a reverse or opposite direction of travel. Thereverse direction of travel may also be termed a rollback condition.

Refer now to FIG. 2 which is a view of the wheel 3 including an axle 6which is mounted to the chassis (not shown) of the vehicle 2 asindicated by the symbol 7. Mounted on the axle 6 is a gear 8 whichrotates with the axle 6 as the vehicle 2 progresses in one direction orthe other along the vehicle travel path 5. A tachometer 9 is secured tothe chassis (not shown) of the vehicle 2 as indicated by the symbol l0,and is operatively engaged with the gear 8 by means of a gear 1 l. Asecond tachometer 12 is secured to the chassis of the vehicle 2 (notshown) as indicated by the symbol l3 and is operatively engaged with thegear 8 by means of a gear 14. The tachometers 9 and 12 are alignedrelative to one another in a predetermined relationship such that if thevehicle is traveling in a forward direction as indicated by the arrow15, an output signal is provided on an output signal lead 16 of thetachometer 9 which is displaced in a first predetermined relationshipfrom the output signal appearing on the output lead 17 of the tachometer12. The second output leads l8 and 19 of the tachometers 9 and 12,respectively, are connected to circuit ground. In the event the vehicle2 is in a rollback condition and is traveling in a reverse direction asindicated by the arrow 20, the output signals appearing at the leads 16and 17 are displaced from one another in a second predetermined phaserelationship. The function of the signals appearing on the leads l6 and17 is to be described shortly. In practice, the tachometers may bemagnetically or optically coupled to the gear 8 rather than mechanicallycoupled as illustrated.

Refer now to FIG. 3 which is a schematic and block diagramrepresentation of the vehicle movement sensing and control apparatus 21which embodies the teachings of the present invention. First and secondswitches such as the transistors 22 and 23 have their base electrodes 24and 25 connected to the signal output leads 17 and 16 of the tachometersl2 and 9, respectively, by way of the current limiting resistors 26 and27, respectively. The collector electrode 28 of the transistor 22 isconnected to a source of operating potential or power, rl-V. The emitterelectrode 29 of the transistor 22 is connected to the collectorelectrode 30 of the transistor 23 through the series connection of asignal storage means such as the primary winding 31 of a transformer 32and also through a current limiting resistor 33. The emitter electrode34 of transistor 23 is connected to circuit ground. The secondarywinding 35 of the signal storage means or transformer 32 has oneterminal connected to circuit ground and the other terminal connected tothe base electrode 36 of an amplifier such as the transistor 37. Theemitter electrode 38 of the transistor 37 is connected to circuit groundand the collector electrode 39 of the transistor 37 is connected to thesource of operating potential +V through 44, and a charge storage devicesuch as the capacitor 45. The output of the detector 41 is connected tothe control terminal 46 of a gate such as the AND gate 47 which has itsinput terminal 48 connected to a signal means such as the oscillator 49.The output of the gate 47 is connected to the signal input 50 of a gatesuch as the AND gate 51. The output of the AND gate 51 is connected byway of a line 52 to an alarm and braking circuit 53. The gate 51 has itscontrol terminal 54 connected to the output of a second detector 55which has its input connected to the common connection of the emitter 29of the transistor 22 and the primary winding 31 of the transformer 32.The detector 55 is comprised of a charge storage device such as thecapacitor 56, a unidirectional current device such as the diode 57, aunidirectional current device such as the diode 58 and a charge storagedevice such as the capacitor 59.

The letters 4A through 4L found on FIG. 3 are the circuit points atwhich the waveshapes illustrated in FIGS. 4 through 4L, respectively,are manifested in the circuitry of FIG. 3. Consider now the operation ofthe vehicle movement sensing and control apparatus 21. As was previouslyexplained, the tachometers 9 and 12 provide on the output leads 16 and17 respectively first and second signals displaced relative to oneanother in a first predetermined phase relationship in response to thevehicle moving in a first direction, for example, a forward direction.In response to the vehicle moving in the opposite or reverse directionthe first and second signals appearing on the leads 16 and 17 aredisplaced relative to one another in a second predetermined phaserelationship. The apparatus 21 provides a vehicle movement controlsignal on the lead 52 to the input of the alarm and braking network 53in response to the apparatus 21 sensing that the first and secondsignals manifested on the leads 16 and 17 are displaced from one anotheraccording to the first predetermined phase relationship. The apparatus21 also includes means for inhibiting the provision of the vehiclemovement control signal on the lead 52 in response to sensing that thefirst and second signals manifested on the leads 16 and 17 are displacedfrom one another according to the second predetermined phaserelationship.

Assume for the moment that the vehicle 2 is traveling in the forwarddirection and the tachometers 9 and 12 are providing first and secondsignals on the leads 16 and 17 which are therefore displaced from oneanother according to the first predetermined phase re1ationship. Forexample, the signal appearing on the lead 16 is a periodic squarewavesignal as illustrated by FIG. 3A and the signal appearing on the lead 17from the tachometer 12 is a periodic square wave signal displaced in afirst predetermined phase relationship, that first predeterminedrelationship being that the first signal state of the output signal fromthe tachometer 9 is 90 in phase ahead of the first signal state of theoutput signal from tachometer 12 (see FIG. 43). At a time the periodicsquarewave signal applied to the base electrode 25 of the transistor 23through the current limiting resistor 27 is at a relatively positivelevel or first signal state such as rl-V. The emitter electrode 34 ofthe transistor 23 is at zero volts since it is connected to circuitground, and the transistor 23 is, therefore, in a condition to becomeconductive (see FIG. 3A). At this time, however, the signal applied tothe base electrode 24 of the transistor 22 (see FIG. 4B) is displaced inphase by 90 from the signal applied to the base electrode of transistor23 and is at a second signal state or a zero volt level which rendersthe transistor 22 nonconductive. This condition, therefore, provides nocircuit path from the source +V to ground and no current flows throughthe common collector-emitter conduction paths of the transistors 22 and23, and through the primary winding 31 of the transformer 32, and thecurrent limiting resistor 33. Since there is no current flow through theprimary winding 31, the detector circuit 55 detects no signal andprovides a zero volt signal to the control input terminal 54 (see FIG.4l) of the gate 51 which in turn disables the gate 51 from providing anoutput signal (see FIG. 4L). Since there is no current flow through theprimary winding 31, there is no signal provided at the base electrode 36of the transistor 37 (see FIG. 4E). Therefore, the detector circuit 41senses no signal output from transistor 37 (see FIG. 4F) and provides azero volt signal to the control terminal 46 of the gate 47 (see FIG. 4G)which disables the gate 47 from providing an output signal. The gates 47and 51, for example, may be AND gates such as described in thepreviously referenced US. Pat. No. 3,600,604. In such an AND gate thereis needed a negative enable signal at the control terminal concurrentwith a periodic signal being provided to the signal input terminal sothat a periodic signal may be produced at the output terminal.

At the time 11 the periodic signal provided to the base electrode 24 ofthe transistor 22 switches to a first signal state or positive signallevel such as +V (see FIG. 4B). This signal makes the transistor 22conductive, and since the signal applied to the base electrode 25 of thetransistor 23 is also at a first signal state or positive level at thistime (see FIG. 4A), the transistors 22 and 23 become concurrentlyconductive and current flows from the source +V through thecollector-emitter path of the transistor 22, the primary winding 31 ofthe transformer 32, the currentlimiting resistor 33 and thecollector-emitter path of the transistor 23 to circuit ground. Currentbegins to increase through the primary winding as illustrated by FIG.4C. In response to the current flow through the emitter electrode of thetransistor 22 the detector circuit 55 functions such that the currentflows through the capacitor 56 and the diode 57 to circuit ground. Thecapacitor 59 remains uncharged at this time since the diode 58 isnonconductive (see FIG. 41). This zero volt signal across capacitor 59then is applied to the control input terminal of the gate 51, anddisables the latter gate. At a time t2 the periodic signal from thetachometer 9 which is applied to the base electrode 25 of the transistor23 returns to a second signal state or a zero volt level and thetransistor 23 is cut off and the series current path through thetransistors 22 and 23 is broken and current is no longer drawn (see FIG.4C). In response to the absence of current fiow through the primarywinding 31 the magnetic field collapses at a rapid rate about thetransformer 32 and voltage is induced in the secondary winding of thetransformer 32 causing current fiow in the secondary winding (see FIG.4D). This voltage increase across the secondary winding is applied tothe base electrode 36 of the transistor 37 (see FIG. 4E), and ispositive enough, for example 0.6 volts, to cause the transistor 37 tobecome conductive and current flows from the source +V through theresistor 40, the collectoremitter path of the transistor 37 to circuitground dropping the voltage at the collector electrode of transistor 37essentially to volts (seeFIG. 4F). The transformer 32, therefore, storedenergy while current flowed through primary winding 31. In response tothe latter current no longer flowing, the field collapsed and the energywas transferred to the base electrode 36 of transistor 37. In responseto the decrease voltage at the col lector electrode of the transistor 37the diode 44 becomes conductive and the voltage at the output plate ofthe capacitor 45 (the junction between the capacitor 45 and diode 44)switches from a Zero volt level to a V level due to the transfer ofcharge from capacitor 42 to capacitor 45. The resultant V enable signalis applied to the terminal 46 of the AND gate 47 for enabling the lattergate (see FIG. 46).

The oscillator 49 is continuously providing a periodic signal (see FIG.4J) to the input signal input terminal 48 of the gate 47 and the gate47, since it is receiving a negative enable signal at its controlledinput terminal, provides at its output a periodic gate output signal.The latter signal in turn is provided to the signal input terminal 50 ofthe gate 51 (see FIG. 4K). This periodic signal is not passed by thegate 51 at this time since its control input terminal 54 is at a zerovolt level.

At the time t3 the periodic signal input to the base electrode 24 of thetransistor 22 again returns to the second signal state or a 0 volt leveland the transistor 22 is biased off. The emitter electrode 29 oftransistor 22 returns to a zero volt level at this time causing diode 58to become conductive whereby charge is transferred from capacitor 56 tocapacitor 59. The resultant charge on capacitor 59 is at a V level,which enables the gate 51. In response thereto a periodic output signalis provided at the output terminal of gate 51. This latter signal (seeFIG. 4L) is a vehicle movement control signal which is supplied to thealarm and braking network 53. In response to the latter signal, thenetwork 53 permits the vehicle 2 to continue along the travel path 5from point A to B (see FIG. 1). The alarm and braking network may be anyknown network which is responsive to an alternating current (AC orperiodic signal input). Such networks are well known in the art and, forexample, may have transformer coupling at the input or any combinationof elements that is responsive only to varying amplitude input signalsat predetermined frequencies. Such latter networks may also take theform of filter circuits. In the event such a periodic signal is notapplied to the input of the alarm and braking network 53, an alarm isactuated and the vehicle is braked. How the apparatus 21 inhibits theprovision of the latter periodic signal and in turn causes the vehicleto be braked is to be described shortly. This condition persists,transistor 22 being biased off until the latter periodic input signalonce again returns to a first signal state or positive voltage level atthe time :5. The enable signals provided to the control input terminals46 and 54 of the gates 47 and 55 respectively remain at negative voltagelevels, however, since the time constants of the detector circuits 41and 55 respectively are chosen such that there is no appreciabledischarge of voltage from the capacitors 45 and 59 as long as the signalinput from the tachometers occurs at the repetition rates asillustrated. At the time t5 the transistors 22 and 23 again becomeconcurrently conductive as was described before, and the systemfunctions in a like manner as previously described.

' At the point in time 60 (see FIG. 4A) the vehicle begins to roll backor travel in a reverse direction for one reason or another, and thesignal outputs of the tachometers 9 and 12 reverse in a predeterminedphase relationship. That is, the first and second signals are displacedfrom one another according to the previously described secondpredetermined phase relationship, that relationship being that the firstsignal state of the output signal from the tachometer 12 is 90 in phaseahead of the first signal state of the output signal from the tachometer9. At the time 16 the input signal to the base electrode 25 oftransistor 23 is at a second signal state or 0 volt level (see FIG. 4A).The transistor 23 is therefore held nonconductive and the seriesconduction path through the primary winding 31 of the transformer 32 isopen irrespective of the first signal state or positive signal levelapplied to the base electrode 24 of the transistor 22 (see FIG. 48). Attime 17 the input signal from the tachometer 9 applied to the baseelectrode 25 of the transistor 23 switches to the first signal state or+V voltage level rendering the transistor 23 conductive. Concurrent withthis there is, as was previously mentioned, also the first signal stateof +V voltage level signal applied to the base electrode 24 of thetransistor 22 and current flows from the source +V to circuit groundthrough the latter transistors and the primary winding 31 of thetransformer 32 and the current limit ing resistor 35. Thecurrent flowthrough the primary winding 31 of the transformer 32 stores energy inthe transformer and is illustrated by FIG. 4C. At the time t8 the inputsignal to the transistor 22 returns to the second signal state or 0volts. This would normally cut the transistor 22 off but since howeverthe primary winding 31 is connected to circuit ground thorugh theconducting transistor 23, the emitter electrode 29 of the transistor 22is driven sufficiently negative by the back electromotive force of thetransformer 32 to keep current flowing through the latter current path.Since the current is still flowing (see FIG. 4C) the collapse of thefield about the transformer 32 does not occur at a rapid enough rate toinduce sufficient voltage at the base electrode 36 and the transistor 37is, therefore, biased off. The collector electrode 39 of the lattertransistor therefore is essentially at a voltage of +V and the diode 44is biased off and the diode 43 is biased on. The voltage on thecapacitor 45 returns to zero volts as the negative voltage is dissipatedby the gate 47. The 0 volts which is now applied to the control terminal46 of the gate 47 biases the gate 47 off and no gate output signal isprovided to the input terminal 50 of the gate 51, in turn there is novehicle movement control signal applied to the alarm and braking network53. In response to the absence of a periodic signal input, the alarm andbraking network 53'applies brakes and stops the vehicle 2. This isirrespective of the control signal applied to the control input terminal54 of the gate 51. It may be seen that this latter control signal is ata zero volt level since the current flow through the primary winding ofthe transformer 31 maintains the diode 57 conductive and the diode 58non-conductive whereby the charge across the capacitor 56 is nottransferred to the capacitor 59. At the time t9 the cycle again repeatsitself as described for the time 27.

In summary, the operation and functionof the apparatus 21 has now beendescribed for both predetermined phase relationships of the tachometeroutput signals. It has been shown that the vehicle movement controlsignal is provided so long as the vehicle is moving in a forwarddirection as manifested by the first and second output signals from thetachometers 9 and 12, respectively, being displaced relative to oneanother in the first predetermined phase relationship. Also, it has beenshown how the vehicle movement control signal has been inhibited and inturn the vehicle braked in the event the output signals from thetachometers 9 and 12 are displaced relative to one another in the secondpredetermined phase relationship, which indicates the vehicle is in aroll-back condition and is traveling in the reverse direction.

I claim:

1. In a system for sensing the direction of movement of a vehicle, thecombination comprising:

a first tachometer means'operative with said vehicle for producing afirst signal in response to the move ment of said vehicle;

a second tachometer means operative with said vehicle for producing asecond signal in response to the movement of said vehicle, said secondsignal being in a first predetermined phase relationship relative tosaid first signal in response to said vehicle moving in a firstdirection, and with said second signal being in a second predeterminedphase relationship relative to said first signal in response to saidvehicle moving in the opposite direction;

first and second switch means having their conduction paths connected inseries, said first switch means closing in response to the production ofsaid first signal, and said second switch means closing in response tothe production of said second signal;

means for providing a .vehicle movement control sig nal in response tosaid first switch means initially closing followed by said second switchmeans closing; and

means for inhibiting the provision of said vehicle movement controlsignal in response to said second switch means initially closingfollowed by said first switch means closing.

2. In a system for sensing the forward and reverse movement of a vehiclealong a vehicle travel path, the combination comprising:

a first tachometer means operative with and aligned with the drive meansof said vehicle for producing a first signal having first and secondsignal states;

a second tachometer means operative with and aligned with the drivemeans of said vehicle for producing a second signal having first andsecond signal states, said second tachometer being aligned relative tosaid first tachometer such that the first signal state of said firstsignal leads the first signal state of said second signal by a firstpredetermined angle when said vehicle is traveling in the forwarddirection, and the first signal state of said second signal leads thefirst signal state of said first signal by a second predetermined angle,which may equal said first predetermined angle when said vehicle istraveling in the reverse direction;

first and second transistors each having base, collector and emitterelectrodes, the base electrode of said first transistor being connectedto said first tachometer means for receiving said first signal, and thebase electrode of said second transistor being connected to said secondtachometer means for receiving said second signal, each of said firstand second transistors being made conductive in response to said firstand second signals being in the first signal state, respectively;

LII

a signal storage means connected in series with the collector-emitterconduction paths of said first and second transistors for storing athird signal in response to said first and second transistors being madeconcurrently conductive; and

signal output means responsive to the storage of said third signal forproviding a vehicle movement control signal.

3. The combination claimed in claim 2 wherein said signal output meanscomprises:

an amplifier means for amplifying the stored third signal for producinga fourth signal;

a first detector means for producing a first enable signal in responseto the provision of said fourth signal;

signal means for providing a periodic signal;

a first gate means having a signal input, a control input, and anoutput, the signal input being connected to said signal means forreceiving said periodic signal, the control input being connected tosaid first detector means for receiving said first enable signal, with afirst gate output signal being provided at the output of said first gatemeans in response to the concurrent provision of said periodic signaland said first enable signal to the signal input and the ocntrol input,respectively; and

means responsive to the provision of said first gate output signal forproviding said vehicle movement control signal.

4. The combination claimed in claim 3 wherein said last-named meanscomprises:

a second detector means operative with said second transistor andresponsive to said second transistor being conductive for providing asecond enable signal;

a second gate means having a signal input connected to the output ofsaid first gate means, a control input operative with said seconddetector means for receiving said second enable signal, and an outputwhere said movement control signal is provided in response to theconcurrent provision of said first gate output signal and said secondenable signal to the signal input and the control input, respectively,of said second gate means.

5. In a system for sensing the direction of movement of a vehicle, thecombination comprising:

means for providing first and second signals displaced relative to oneanother in a first predetermined phase relationship in response to saidvehicle moving in a first direction, with said first and second signalsbeing displaced relative to one another in a second predetermined phaserelationship in response to said vehicle moving in the oppositedirection;

first and second switch means having their conduction paths connected inseries, said first switch means closing in response to the production ofsaid first signal, and said second switch means closing in response tothe production of said second signal;

means for providing a vehicle movement control signal in response tosaid first switch means initially closing followed by said second switchmeans closing; and

means for inhibiting the provision of said vehicle movement controlsignal in response to said second switch means initially closingfollowed by said first switch means closing.

In a system for sensing the forward and reverse movement of a vehiclealong a vehicle travel path, the combination comprising:

rst means operative-with said vehicle for producing a first signalhaving first and second signal states;

second means operative with said vehicle for producing a second signalhaving first and second signal states, with the first signal state ofsaid first signal leading the first signal state of said second signalby a first phase angle when said vehicle is traveling in the forwarddirection, and the first signal state of said second signal leads thefirst signal state of said first signal by a second phase angle whensaid vehicle is traveling in the reverse direction;

rst and second transistors each having base, collector and emitterelectrodes, the base electrode of said first transistor being operativewith said first means for receiving said first signal, and the baseelectrode of said second transistor being operative signal storage meanscomprises a transformer.

8. The combination claimed in claim 7, wherein said means, responsive tothe storage of said third signal includes a detector.

1. In a system for sensing the direction of movement of a vehicle, thecombination comprising: a first tachometer means operative with saidvehicle for producing a first signal in response to the movement of saidvehicle; a second tachometer means operative with said vehicle forproducing a second signal in response to the movement of said vehicle,said second signal being in a first predetermined phase relationshiprelative to said first signal in response to said vehicle moving in afirst direction, and with said second signal being in a secondpredetermined phase relationship relative to said first signal inresponse to said vehicle moving in the opposite direction; first andsecond switch means having their conduction paths connected in series,said first switch means closing in response to the production of saidfirst signal, and said second switch means closing in response to theproduction of said second signal; means for providing a vehicle movementcontrol signal in response to said first switch means initially closingfollowed by said second switch means closing; and means for inhibitingthe provision of said vehicle movement control signal in response tosaid second switch means initially closing followed by said first switchmeans closing.
 2. In a system for sensing the forward and reversemovement of a vehicle along a vehicle travel path, the combinationcomprising: a first tachometer means operative with and aligned with thedrive means of said vehicle for producing a first signal having firstand second signal states; a second tachometer means operative with andaligned with the drive means of said vehicle for producing a secondsignal having first and second signal states, said second tachometerbeing aligned relative to said first tachometer such that the firstsignal state of said first signal leads the first signal state of saidsecond signal by a first predetermined angle when said vehicle istraveling in the forward direction, and the first signal state of saidsecond signal leads the first signal state of said first signal by asecond predetermined angle, which may equal said first predeterminedangle when said vehicle is traveling in the reverse direction; first andsecond transistors each having base, collector and emitter electrodes,the base electrode of said first transistor being connected to saidfirst tachometer means for receiving said first signal, and the baseelectrode of said second transistor being connected to said secondtachometer means for receiving said second signal, each of said firstand second transistors being made conductive in response to said firstand second signals being in the first signal state, respectively; asignal storage means connected in series with the collector-emitterconduction paths of said first and second transistors for storing athird signal in response to said first and second transistors being madeconcurrently conductive; and signal output means responsive to thestorage of said third signal for providing a vehicle movement controlsignal.
 3. The combination claimed in claim 2 wherein said signal outputmeans comprises: an amplifier means for amplifying the stored thirdsignal for producing a fourth signal; a first detector means forproducing a first enable signal in response to the provision of saidfourth signal; signal means for providing a periodic signal; a firstgate means having a signal input, a control input, and an output, thesignal input being connected to said signal means for receiving saidperiodic signal, the control input being connected to said firstdetector means for receiving said first enable signal, with a first gateoutput signal being provided at the output of said first gate means inresponse to the concurrent provision of said periodic signal and saidfirst enable signal to the signal input and the ocntrol input,respectively; and means responsive to the provision of said first gateoutput signal for providing said vehicle movement control signal.
 4. Thecombination claimed in claim 3 wherEin said last-named means comprises:a second detector means operative with said second transistor andresponsive to said second transistor being conductive for providing asecond enable signal; a second gate means having a signal inputconnected to the output of said first gate means, a control inputoperative with said second detector means for receiving said secondenable signal, and an output where said movement control signal isprovided in response to the concurrent provision of said first gateoutput signal and said second enable signal to the signal input and thecontrol input, respectively, of said second gate means.
 5. In a systemfor sensing the direction of movement of a vehicle, the combinationcomprising: means for providing first and second signals displacedrelative to one another in a first predetermined phase relationship inresponse to said vehicle moving in a first direction, with said firstand second signals being displaced relative to one another in a secondpredetermined phase relationship in response to said vehicle moving inthe opposite direction; first and second switch means having theirconduction paths connected in series, said first switch means closing inresponse to the production of said first signal, and said second switchmeans closing in response to the production of said second signal; meansfor providing a vehicle movement control signal in response to saidfirst switch means initially closing followed by said second switchmeans closing; and means for inhibiting the provision of said vehiclemovement control signal in response to said second switch meansinitially closing followed by said first switch means closing.
 6. In asystem for sensing the forward and reverse movement of a vehicle along avehicle travel path, the combination comprising: first means operativewith said vehicle for producing a first signal having first and secondsignal states; second means operative with said vehicle for producing asecond signal having first and second signal states, with the firstsignal state of said first signal leading the first signal state of saidsecond signal by a first phase angle when said vehicle is traveling inthe forward direction, and the first signal state of said second signalleads the first signal state of said first signal by a second phaseangle when said vehicle is traveling in the reverse direction; first andsecond transistors each having base, collector and emitter electrodes,the base electrode of said first transistor being operative with saidfirst means for receiving said first signal, and the base electrode ofsaid second transistor being operative with said second means forreceiving said second signal, each of said first and second transistorsbeing made conductive in response to said first and second signals beingin the first signal state, respectively; a signal storage meansconnected in series with the collector-emitter conduction path of saidfirst and second transistors for storing a third signal in response tosaid first and second transistors becoming concurrently conductive; andmeans responsive to the storage of said third signal for providing avehicle movement control signal.
 7. The combination claimed in claim 6,wherein said signal storage means comprises a transformer.
 8. Thecombination claimed in claim 7, wherein said means responsive to thestorage of said third signal includes a detector.